Hubbard band versus oxygen vacancy states in the correlated electron metal SrVO3

Strong electron correlations in solids are at the heart of fascinating phenomena such as high temperature superconductivity, whose understanding remains a prominent open problem in Physics. A central prediction of dynamical mean field theory (DMFT) is the breaking of Landau's Fermi liquid, which describes extremely well simple metals like copper, into itinerant heavy quasiparticles and localized Mott-Hubbard states. To test it, electronic structure calculations based on DMFT are usually benchmarked against the photoemission spectra of SrVO${}_{3}$, a cubic perovskite with one $d$ electron per unit cell that is considered the gold standard in this field. However, the present study shows that the UV synchrotron radiation used in the photoemission experiments creates oxygen vacancies, resulting in a strong peak of defect states essentially on top of the SrVO${}_{3}$ Hubbard band. As recent works found that the same peak of vacancy states occurs in noncorrelated wide-gap ${d}^{0}$insulators, such as SrTiO${}_{3}$, an unavoidable worry emerges. What if the putative Hubbard bands observed in SrVO${}_{3}$ were just a mirage? What if this strongly correlated effect, a hallmark prediction of DMFT for the past 25 years was just not there? This study thoroughly explores those crucial issues both experimentally and theoretically.